THEAETETUS: I do not as yet understand you.
SOCRATES: Then I will try to explain myself: just now we asked the question, whether a man who had learned and remembered could fail to know, and we showed that a person who had seen might remember when he had his eyes shut and could not see, and then he would at the same time remember and not know. But this was an impossibility. And so the Protagorean fable came to nought, and yours also, who maintained that knowledge is the same as perception.
THEAETETUS: True.
SOCRATES: And yet, my friend, I rather suspect that the result would have been different if Protagoras, who was the father of the first of the two brats, had been alive; he would have had a great deal to say on their behalf. But he is dead, and we insult over his orphan child; and even the guardians whom he left, and of whom our friend Theodorus is one, are unwilling to give any help, and therefore I suppose that I must take up his cause myself, and see justice done?
THEODORUS: Not I, Socrates, but rather Callias, the son of Hipponicus, is guardian of his orphans. I was too soon diverted from the abstractions of dialectic to geometry. Nevertheless, I shall be grateful to you if you assist him.
SOCRATES: Very good, Theodorus; you shall see how I will come to the rescue. If a person does not attend to the meaning of terms as they are commonly used in argument, he may be involved even in greater paradoxes than these. Shall I explain this matter to you or to Theaetetus?
THEODORUS: To both of us, and let the younger answer; he will incur less disgrace if he is discomfited.
SOCRATES: Then now let me ask the awful question, which is this:—Can a man know and also not know that which he knows?
THEODORUS: How shall we answer, Theaetetus?
THEAETETUS: He cannot, I should say.